diff --git a/manual/introduction.md b/manual/introduction.md
index d470f08..166b4de 100644
--- a/manual/introduction.md
+++ b/manual/introduction.md
@@ -34,8 +34,8 @@ Create a routing table:
 Note that you can populate the `trail.Path()` data structure yourself and use it in place of its string counterpart. This is useful if you are using a third-party routing library which already provides you with a deconstructed URL:
 <listing id="parse-path">
 
-Define a custom argument type:
-<listing id="custom-arg">
+Define a custom codec that can be used in arguments, parameters and fragments:
+<listing id="custom-codec">
 
 Define a custom path element type:
 <listing id="custom-path-elem">
diff --git a/manual/listings.json b/manual/listings.json
index bc75079..018d1be 100644
--- a/manual/listings.json
+++ b/manual/listings.json
@@ -14,11 +14,6 @@
     "language" : "scala",
     "result" : "user: hello, show: false"
   },
-  "custom-arg" : {
-    "code" : "import scala.util.Try\nimplicit case object IntSetArg extends Codec[Set[Int]] {\n  override def encode(s: Set[Int]): Option[String] = Some(s.mkString(\",\"))\n  override def decode(s: Option[String]): Option[Set[Int]] =\n    s.flatMap(value => Try(value.split(',').map(_.toInt).toSet).toOption)\n}\n\nval export = Root / \"export\" / Arg[Set[Int]]\nprintln(export.url(Set(1, 2, 3)))",
-    "language" : "scala",
-    "result" : "/export/1,2,3"
-  },
   "query-params-opt" : {
     "code" : "val routeParamsOpt = Root / \"details\" & Param[Int](\"id\") & Param[Option[Boolean]](\"show\")\nprintln(routeParamsOpt.parse(\"/details?id=42\"))",
     "language" : "scala",
@@ -44,6 +39,11 @@
     "language" : "scala",
     "result" : "/asdf"
   },
+  "custom-codec" : {
+    "code" : "import scala.util.Try\nimplicit case object IntSetCodec extends Codec[Set[Int]] {\n  override def encode(s: Set[Int]): Option[String] = Some(s.mkString(\",\"))\n  override def decode(s: Option[String]): Option[Set[Int]] =\n    s.flatMap(value =>\n      if (value.isEmpty) Some(Set())\n      else Try(value.split(',').map(_.toInt).toSet).toOption)\n}\n\nval export = Root / \"export\" / Arg[Set[Int]]\nprintln(export.url(Set(1, 2, 3)))",
+    "language" : "scala",
+    "result" : "/export/1,2,3"
+  },
   "query-fragment" : {
     "code" : "val routeFragment = Root $ Fragment[Int]\nprintln(routeFragment.parse(\"/#42\"))",
     "language" : "scala",
diff --git a/manual/src/main/scala/trail/manual/Listings.scala b/manual/src/main/scala/trail/manual/Listings.scala
index beb4c56..ac6d7c1 100644
--- a/manual/src/main/scala/trail/manual/Listings.scala
+++ b/manual/src/main/scala/trail/manual/Listings.scala
@@ -46,12 +46,14 @@ object Listings extends App {
   }
   println(result2)
 
-  listing("custom-arg")
+  listing("custom-codec")
   import scala.util.Try
-  implicit case object IntSetArg extends Codec[Set[Int]] {
+  implicit case object IntSetCodec extends Codec[Set[Int]] {
     override def encode(s: Set[Int]): Option[String] = Some(s.mkString(","))
     override def decode(s: Option[String]): Option[Set[Int]] =
-      s.flatMap(value => Try(value.split(',').map(_.toInt).toSet).toOption)
+      s.flatMap(value =>
+        if (value.isEmpty) Some(Set())
+        else Try(value.split(',').map(_.toInt).toSet).toOption)
   }
 
   val export = Root / "export" / Arg[Set[Int]]
diff --git a/shared/src/main/scala/trail/Path.scala b/shared/src/main/scala/trail/Path.scala
index 99fad25..5ffb41f 100644
--- a/shared/src/main/scala/trail/Path.scala
+++ b/shared/src/main/scala/trail/Path.scala
@@ -20,9 +20,9 @@ object PathParser {
 
   def parseArgs(query: String): List[(String, String)] =
     query.split('&').flatMap { x =>
-      val pair = x.split('=')
-      if (pair.length != 2) List.empty
-      else List((pair(0), URI.decode(pair(1))))
+      val equalSign = x.indexOf('=')
+      if (equalSign == -1) List()
+      else List((x.take(equalSign), URI.decode(x.drop(equalSign + 1))))
     }.toList
 
   /** Return URL without scheme and authority */
diff --git a/shared/src/test/scala/trail/PathTests.scala b/shared/src/test/scala/trail/PathTests.scala
index 5bdb10a..763a928 100644
--- a/shared/src/test/scala/trail/PathTests.scala
+++ b/shared/src/test/scala/trail/PathTests.scala
@@ -60,4 +60,10 @@ class PathTests extends FunSuite {
       assert(parsed.url == url)
     }
   }
+
+  test("Parse argument with empty value") {
+    val url = "/test?a="
+    assert(PathParser.parse(url).path == "/test")
+    assert(PathParser.parse(url).args == List("a" -> ""))
+  }
 }
\ No newline at end of file
diff --git a/shared/src/test/scala/trail/RouteParseTests.scala b/shared/src/test/scala/trail/RouteParseTests.scala
index e1cb3ce..ea17d32 100644
--- a/shared/src/test/scala/trail/RouteParseTests.scala
+++ b/shared/src/test/scala/trail/RouteParseTests.scala
@@ -2,6 +2,8 @@ package trail
 
 import org.scalatest._
 
+import scala.util.Try
+
 class RouteParseTests extends FunSpec with Matchers {
   it("Parse root") {
     val root = Root
@@ -58,4 +60,19 @@ class RouteParseTests extends FunSpec with Matchers {
     assert(userInfo.parse("/user/hello/false")
       .contains(("hello", false)))
   }
+
+  it("Set codec") {
+    implicit case object LongSetCodec extends Codec[Set[Long]] {
+      override def encode(s: Set[Long]): Option[String] = Some(s.mkString(","))
+      override def decode(s: Option[String]): Option[Set[Long]] =
+        s.flatMap(value =>
+          if (value.isEmpty) Some(Set())
+          else Try(value.split(',').map(_.toLong).toSet).toOption)
+    }
+
+    val route = Root / "size" & Param[Set[Long]]("folders")
+    assert(route.parse(route(Set[Long]())).contains(Set[Long]()))
+    assert(route.parse(route(Set[Long](1))).contains(Set[Long](1)))
+    assert(route.parse(route(Set[Long](1, 2, 3))).contains(Set[Long](1, 2, 3)))
+  }
 }